Classes
struct	Times
	Modelled UT1 and TT at the same instant, in Julian days. More...

Enumerations
enum class	Scale : uint8_t { UTC , UT1 }
	The explicitly declared scale of a civil datetime. More...

Functions
auto	ut1_to_jd (const calendar::Datetime &ut1_dt) -> double
	Convert UT1 datetime to julian day number.
auto	jd_to_ut1 (const double jd) -> calendar::Datetime
	Convert julian day number to UT1 datetime.
auto	tt_to_jde (const calendar::Datetime &tt_dt) -> double
	Converts a TT datetime to julian ephemeris day number.
auto	jde_to_tt (const double jde) -> calendar::Datetime
	Converts a julian ephemeris day number to TT datetime.
auto	civil_to_tt (const calendar::Datetime &civil_dt, const Scale scale, const astro::delta_t::Model model=astro::delta_t::DEFAULT_MODEL) -> calendar::Datetime
	Convert one explicitly scaled civil datetime to TT, with strict modern UTC admission.
auto	resolve_times (const calendar::Datetime &civil_dt, const Scale scale, const astro::delta_t::Model model=astro::delta_t::DEFAULT_MODEL) -> Times
	Resolve UT1 and TT without additional civil-year or derived-TT admission policy.
auto	jde_to_ut1 (const double jde) -> calendar::Datetime
	Converts a julian ephemeris day number to UT1 datetime.
auto	ut1_to_jde (const calendar::Datetime &ut1_dt) -> double
	Converts a UT1 datetime to julian ephemeris day number.
auto	jde_to_utc (const double jde) -> calendar::Datetime
	Converts a julian ephemeris day number to UTC datetime.
auto	utc_to_jde (const calendar::Datetime &utc_dt) -> double
	Converts a UTC datetime to julian ephemeris day number.
auto	utc_year_start_jde (const std::chrono::year year) -> double
	Return the JDE(TT) of January 1 at 00:00 UTC in a calendar year.
auto	validate_annual_year (const int32_t year) -> void
	Validate a Gregorian year for an annual (whole-year) query.
auto	utc_year_jde_window (const int32_t year) -> std::array< double, 2 >
	Return the half-open UTC year window expressed as JDE(TT) bounds.
constexpr auto	jde_to_jm (const double jde) -> double
	Converts a julian ephemeris day number to julian millennium.
constexpr auto	jm_to_jde (const double jm) -> double
	Converts a julian millennium to julian ephemeris day number.
constexpr auto	jde_to_jc (const double jde) -> double
	Converts a julian ephemeris day number to julian century.
constexpr auto	jc_to_jde (const double jc) -> double
	Converts a julian century to julian ephemeris day number.

Variables
constexpr double	J2000
	The julian day number of 2000-01-01, 12:00:00.0 (noon).
constexpr double	DAYS_PER_JULIAN_CENTURY
	The number of days in one Julian century (36525 days).

Enumeration Type Documentation

◆ Scale

enum class astro::julian_day::Scale : uint8_t

strong

The explicitly declared scale of a civil datetime.

Enumerator
UTC
UT1

Function Documentation

◆ civil_to_tt()

auto astro::julian_day::civil_to_tt	(	const calendar::Datetime &	civil_dt,
		const Scale	scale,
		const astro::delta_t::Model	model = astro::delta_t::DEFAULT_MODEL )->calendar::Datetime

inlinenodiscard

Convert one explicitly scaled civil datetime to TT, with strict modern UTC admission.

Parameters

civil_dt	A valid civil datetime, without an inserted leap second.
scale	UTC from 1972-01-01, or explicitly labelled UT1.
model	Delta T model for UT1 input; UTC-to-TT does not evaluate Delta T.

Returns: The TT datetime. Future UTC holds the last known TAI-minus-UTC table entry.

Exceptions

std::invalid_argument For invalid input, model-domain rejection or an unrepresentable shift.

◆ jc_to_jde()

auto astro::julian_day::jc_to_jde ( const double jc ) ->double

nodiscardconstexpr

Converts a julian century to julian ephemeris day number.

Parameters

jc	The julian century since J2000.

Returns: The julian ephemeris day number, which is based on TT.

◆ jd_to_ut1()

auto astro::julian_day::jd_to_ut1 ( const double jd ) ->calendar::Datetime

inlinenodiscard

Convert julian day number to UT1 datetime.

Parameters

jd	The julian day number.

Returns: The datetime in UT1.

Exceptions

std::invalid_argument if jd is not finite, beyond the year_month_day-representable years, or the estimated gregorian year is < 401.

Note: ut1_to_jd(32767-12-31, fraction ≈ 1) rounds up to exactly the upper bound 13689325.5, which this function rejects — a 1-ulp round-trip break callers must expect.

See also: ERFA v2.0.1 src/jd2cal.c, eraJd2cal.

◆ jde_to_jc()

auto astro::julian_day::jde_to_jc ( const double jde ) ->double

nodiscardconstexpr

Converts a julian ephemeris day number to julian century.

Parameters

jde	The julian ephemeris day number, which is based on TT.

Returns: The julian century since J2000.

◆ jde_to_jm()

auto astro::julian_day::jde_to_jm ( const double jde ) ->double

nodiscardconstexpr

Converts a julian ephemeris day number to julian millennium.

Parameters

jde	The julian ephemeris day number, which is based on TT.

Returns: The julian millennium since J2000.

See also: ERFA v2.0.1 erfam.h, ERFA_DJM.

◆ jde_to_tt()

auto astro::julian_day::jde_to_tt ( const double jde ) ->calendar::Datetime

inlinenodiscard

Converts a julian ephemeris day number to TT datetime.

Parameters

jde	The julian ephemeris day number, which is based on TT (not UT1).

Returns: The date and time, in TT.

◆ jde_to_ut1()

auto astro::julian_day::jde_to_ut1 ( const double jde ) ->calendar::Datetime

inlinenodiscard

Converts a julian ephemeris day number to UT1 datetime.

Parameters

jde	The julian ephemeris day number, which is based on TT.

Returns: The date and time, in UT1.

◆ jde_to_utc()

auto astro::julian_day::jde_to_utc ( const double jde ) ->calendar::Datetime

inlinenodiscard

Converts a julian ephemeris day number to UTC datetime.

Parameters

jde	The julian ephemeris day number, which is based on TT.

Returns: The date and time, in UTC.

Note: Before modern UTC (1972-01-01) this degrades to UT1; see astro::leap_second::tt_to_utc.

◆ jm_to_jde()

auto astro::julian_day::jm_to_jde ( const double jm ) ->double

nodiscardconstexpr

Converts a julian millennium to julian ephemeris day number.

Parameters

jm	The julian millennium since J2000.

Returns: The julian ephemeris day number, which is based on TT.

See also: ERFA v2.0.1 erfam.h, ERFA_DJM.

◆ resolve_times()

auto astro::julian_day::resolve_times	(	const calendar::Datetime &	civil_dt,
		const Scale	scale,
		const astro::delta_t::Model	model = astro::delta_t::DEFAULT_MODEL )->Times

inlinenodiscard

Resolve UT1 and TT without additional civil-year or derived-TT admission policy.

Parameters

civil_dt	A valid civil datetime on the declared scale.
scale	UTC from 1972-01-01, or explicitly labelled UT1.
model	The selected Delta T model.

Returns: Both scales; UT1 input passes through without a reverse conversion.

Exceptions

std::invalid_argument For invalid input, model-domain rejection or an unrepresentable shift.

Note: Model guards apply at the evaluation instant: UT1 for the forward shift, TT for the reverse. Algo4 UT1 input can derive TT beyond its TT-evaluation end; reversing that TT may fail.

◆ tt_to_jde()

auto astro::julian_day::tt_to_jde ( const calendar::Datetime & tt_dt ) ->double

inlinenodiscard

Converts a TT datetime to julian ephemeris day number.

Parameters

tt_dt The date and time (TT).

Returns: The julian ephemeris day number, which is based on TT (not UT1).

◆ ut1_to_jd()

auto astro::julian_day::ut1_to_jd ( const calendar::Datetime & ut1_dt ) ->double

inlinenodiscard

Convert UT1 datetime to julian day number.

Parameters

ut1_dt The datetime in UT1.

Returns: The julian day number.

Exceptions

std::invalid_argument if the gregorian year is < 1.

Note: Years 1-400 convert forward, but sit below jd_to_ut1's year-401 bound — round-trips only close from 401-01-01 onwards.

See also: ERFA v2.0.1 src/cal2jd.c, eraCal2jd.

◆ ut1_to_jde()

auto astro::julian_day::ut1_to_jde ( const calendar::Datetime & ut1_dt ) ->double

inlinenodiscard

Converts a UT1 datetime to julian ephemeris day number.

Parameters

ut1_dt The date and time, in UT1.

Returns: The julian ephemeris day number, which is based on TT.

Exceptions

std::invalid_argument If the datetime is invalid, the TT shift leaves the representable years, or the converted TT year is below 1; see ut1_to_jd.

◆ utc_to_jde()

auto astro::julian_day::utc_to_jde ( const calendar::Datetime & utc_dt ) ->double

inlinenodiscard

Converts a UTC datetime to julian ephemeris day number.

Parameters

utc_dt The date and time, in UTC.

Returns: The julian ephemeris day number, which is based on TT.

Exceptions

std::invalid_argument If a pre-1972 datetime is invalid, the UTC-to-TT shift leaves the representable years, or the converted TT year is below 1; see astro::leap_second::utc_to_tt and ut1_to_jd.

Note: Before modern UTC (1972-01-01) this degrades to UT1; see astro::leap_second::utc_to_tt.

◆ utc_year_jde_window()

auto astro::julian_day::utc_year_jde_window ( const int32_t year ) ->std::array< double, 2 >

inlinenodiscard

Return the half-open UTC year window expressed as JDE(TT) bounds.

Parameters

year	Gregorian year in [1, 32766], leaving the next January 1 representable.

Returns: Inclusive start and exclusive end, in that order.

Exceptions

std::invalid_argument If the year leaves [1, 32766].

Note: Before 1972 the UTC conversion uses UT1; see utc_to_jde.

◆ utc_year_start_jde()

auto astro::julian_day::utc_year_start_jde ( const std::chrono::year year ) ->double

inlinenodiscard

Return the JDE(TT) of January 1 at 00:00 UTC in a calendar year.

Parameters

year	Gregorian year in [1, 32767].

Returns: The UTC year boundary expressed in TT.

Exceptions

std::invalid_argument If the calendar year is invalid or below 1; see ut1_to_jd.

Note: Before 1972 this uses the UT1 substitute from utc_to_jde.

See also: utc_to_jde

◆ validate_annual_year()

auto astro::julian_day::validate_annual_year ( const int32_t year ) ->void

inline

Validate a Gregorian year for an annual (whole-year) query.

Parameters

year	The original integer year.

Exceptions

std::invalid_argument If year leaves [1, 32766].

Note: The ceiling sits one below std::chrono::year::max() so the next January 1 stays representable.

Variable Documentation

◆ DAYS_PER_JULIAN_CENTURY

double astro::julian_day::DAYS_PER_JULIAN_CENTURY

inlineconstexpr

The number of days in one Julian century (36525 days).

See also: ERFA v2.0.1 erfam.h, ERFA_DJC.

◆ J2000

double astro::julian_day::J2000

inlineconstexpr

The julian day number of 2000-01-01, 12:00:00.0 (noon).

See also: ERFA v2.0.1 erfam.h, ERFA_DJ00.

Classes

Enumerations

Functions

Variables

Enumeration Type Documentation

◆ Scale

Function Documentation

◆ civil_to_tt()

◆ jc_to_jde()

◆ jd_to_ut1()

◆ jde_to_jc()

◆ jde_to_jm()

◆ jde_to_tt()

◆ jde_to_ut1()

◆ jde_to_utc()

◆ jm_to_jde()

◆ resolve_times()

◆ tt_to_jde()

◆ ut1_to_jd()

◆ ut1_to_jde()

◆ utc_to_jde()

◆ utc_year_jde_window()

◆ utc_year_start_jde()

◆ validate_annual_year()

Variable Documentation

◆ DAYS_PER_JULIAN_CENTURY

◆ J2000